Evaporative heat exchanger for cooling a refrigerant

ABSTRACT

An evaporative heat exchanger for cooling a hot refrigerant having a core of alternatively stacked dry and wet plates. Each dry plate includes a dry side defining a plurality of dry channels in a first direction, a series of ports distributed along the dry channels, a wet side, and a refrigerant cooling section. Each wet plate includes a wet side adjacent to and cooperates with the wet side of the dry plate to define a plurality of wet channels in a second direction. The dry channels, ports, and wet channels define a labyrinth for the air flow, which evaporates the liquid contained in the wet channels resulting in a cooling of the refrigerant. The refrigerant cooling section is integral with the outboard of the dry plate and adjacent to an end section of the wet channels to provide enhanced refrigerant cooling.

TECHNICAL FIELD OF INVENTION

The invention relates to an evaporative heat exchanger for cooling a refrigerant; more specifically, to an evaporative heat exchanger having an integrated outboard refrigerant cooling section.

BACKGROUND OF INVENTION

An indirect evaporative cooler is a heat exchange device comprising a dry air stream and a wet air stream flowing in two separate sets of channels. The heat from the dry air stream is conducted across the dry channel walls to the wet air stream in the wet channels. This heat causes evaporation of the liquid water in the wet air stream resulting in cooling of the dry air stream and humidification of the wet air stream. The cooling of the dry air stream is alluded to as the indirect evaporative cooling of the air since the dry air stream does not come in direct contact with the evaporating water. In an indirect evaporative cooler there is also cooling of the wet air stream in addition to humidification. This is referred to as the direct evaporative cooling of the air since in this case there is a direct contact between the air and the evaporating water.

An indirect evaporative cooler can be employed to cool the condenser of a vapor compression refrigeration or air conditioning system. The vapor compression system comprises a condenser, an expansion device, an evaporator and a compressor. The working fluid of the vapor compression system is a refrigerant, such as R-134a, which is capable of undergoing liquid-to-vapor transformation in the evaporator and vapor-to-liquid transformation in the condenser. The compressor—located between the evaporator and the condenser—provides the motive power for the circulation of the refrigerant in a closed loop and the expansion device—located between the condenser and the evaporator—causes expansion of the high pressure mixture of liquid-vapor refrigerant from the condenser into the evaporator.

The most common method of condensing the refrigerant in the condenser is by forcing the ambient air through the fins on the exterior of the condenser. The ambient air at relatively high temperature is not as effective as cooler air in condensing the refrigerant. Another common method of condensing the refrigerant in the condenser is by spraying liquid water on the exterior of the condenser. A drawback of this method is that the water consumption is excessive. Motivated by these considerations evaporatively cooled air is utilized to condense the refrigerant vapor.

Shown in FIG. 1 is an evaporative cooler 10 that includes a stack 12 of alternating wet and dry plates having features that cooperate with each other to define a labyrinth for air and water flow. A stream of ambient air 14 is introduced at one end of stack 12, wherein the air 14 is split into working stream 16 and a product stream 18 and directly cools the working air stream 16 while humidifying it. Working stream 16 evaporates water 19 which in turn indirectly cools product stream 18. The cooled product stream 18 is used for cooling purposes whereas the wet working stream 16 is either exhausted to outside ambient air or used primarily for humidification purposes. The alternating stacked plates are formed of a plastic or cellulose material.

It has been proposed to provide a condenser cooling concept that utilizes the principle of evaporating a liquid to cool a hot refrigerant, which has a higher pressure than ambient air. To contain the higher pressure refrigerant, the refrigerant channels are formed of a higher strength heat transfer material such as aluminum to provide the structural integrity required. The wet and dry channels of the associated evaporative cooler are formed of a plastic or cellulose material. Working air is passed through the refrigerant condenser, which includes a complex network of wet and dry channels inter crossed with the refrigerant channels, incrementally cooling the refrigerant. The refrigerant channels are bundled near the center of the evaporative cooler, thereby, limiting the heat transfer area for evaporative cooling.

There exists a need for an evaporatively cooled condenser that may provide improved heat transfer efficiency for cooling a refrigerant; there also exists a need for an evaporative cooler that can accommodate a high pressure refrigerant. There is also a need for an evaporatively cooled condenser that is simpler and cost effective to manufacture; and there is a further need for an evaporatively cooled condenser that is scalable in size.

SUMMARY OF THE INVENTION

The present invention provides an evaporatively cooled condenser that includes a stack of alternating wet and dry plates that utilizes the principles of evaporative cooling to remove heat from a hot refrigerant with a higher than ambient pressure.

The evaporative heat exchanger includes a dry plate having an air flow section and an integral refrigeration cooling section. The air flow section includes a dry side that defines a plurality of dry channels in a first direction, a wet side, and a series of varying sized ports for air distribution located along the bottom of the dry channel. The outboard refrigerant cooling section has refrigerant passageways and is structurally integral with the air flow section to provide efficient thermal conductivity for heat transfer.

The evaporative heat exchanger also includes a wet plate having a wet surface that is adjacent to and cooperates with the wet side of the dry plate to define a plurality of wet air flow conduits in a second direction, which is substantially perpendicular to the first direction. The wet air flow conduits are adapted to contain an evaporative liquid such as water capable of undergoing liquid-to-vapor transformation. Each wet plate further includes a dry surface adjacent to and cooperates with the dry side of the next alternatively stacked dry plate to define a plurality of dry air flow conduits in the first direction. The wet flow conduits communicate with the dry air flow conduits through the ports.

An evaporative liquid, such as water, is provided to the wet plates. Concurrently, an air stream of low humidity is induced through the heat exchanger core defined by the stack of wet and dry plate. As the low humidity air evaporates the liquid provided to the surface of wet plate, the temperatures of the liquid and wet and dry plates are reduced due to removal of latent heat therefrom resulting in evaporation of water from liquid to vapor state. The cooling of the heat exchanger in turn removes heat from the hot refrigerant flowing in the passageways of the integral outboard refrigerant cooling section

Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

This invention will be further described with reference to the accompanying drawings in which:

FIG. 1 shows a perspective view of a prior art evaporative cooler depicting schematically the flow direction of air stream and evaporative liquid stream.

FIG. 2 shows a perspective view of evaporative cooler having end headers connected to refrigerant cooling section and depicting schematically the flow pattern of the air stream and evaporative liquid stream.

FIG. 3 shows an expanded perspective view of the stacked plates forming the evaporative cooler.

FIG. 4 shows a perspective view of the evaporative cooler stacked plates schematically depicting the flow pattern of the air stream, evaporative liquid stream, and the refrigerant stream.

FIGS. 5 A-C show integral evaporative cooling section and alternative embodiments of heat transfer fins located on the dry plates.

FIG. 6 shows a detailed view of the evaporative liquid distribution conduit.

FIG. 7 shows a perspective view of an alternative embodiment of an evaporative cooler having an end refrigerant cooling section.

DETAILED DESCRIPTION OF INVENTION

Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, an evaporative refrigerant cooler 90 constructed in accordance with the subject invention, is generally shown in FIG. 2. Evaporative refrigerant cooler 90 includes a stack of alternating wet and dry plates 100, 200 that utilizes the principle of evaporative cooling to remove heat from a hot refrigerant. In reference to FIG. 3, each dry plate 200 has an outboard integrated refrigerant cooling section 600. Both wet and dry plates 100, 200 have unique features-which cooperate with each other to define a labyrinth for air flow for optimal evaporative cooling of refrigerant flowing in refrigerant cooling section 600. An evaporative liquid, such as water, is provided to wet plates 100. Referring back to FIG. 2, an air stream 500 of low humidity is induced through the stack of wet and dry plates 100, 200. As air stream 500 evaporates the liquid provided to the surface of wet plate 100, the temperatures of the wet and dry plates 100, 200 as well as the air stream are reduced due to the removal of heat by the evaporating liquid. This in turn removes heat from the refrigerant vapor condensing it to liquid state. The inventive features of evaporative refrigerant cooler 90 for removing heat form the hot refrigerant will be better appreciated following the detailed discussion herein below.

In reference to FIG. 3, a stack of alternating wet and dry plates 100, 200 forms core 15 of evaporative refrigerant cooler 90. The total number of alternating wet and dry plates required depends on the cooling needs of the hot refrigerant. However, at least one wet plate 100 and one dry plate 200 are required to form core 15. For discussion purposes and for clarity of illustration, wet plate 100 and dry plate 200 are shown detached and expanded from the core 15. Core 15 has a substantially center longitudinal axis 20 extending in first direction A and opposing second direction B. Core 15 also has a substantially central latitudinal axis 25 extending in third direction C and opposing fourth direction D. Latitudinal axis 25 is substantially perpendicular to longitudinal axis 20. The length of core 15 extends along longitudinal axis 20 and the width of core 15 extends along latitudinal axis 25.

Protruding from wet surface 110 of wet plate 100 is a plurality of substantially parallel channel guides 115 that extends the width of core 15. Channel guides 115 cooperate with wet surface 110 to define a series of substantially parallel wet channels 125. Wet channels 125 have opposing ends 130 c, 130 d located outboard of core 15 in the third and fourth directions C, D. The opposing ends 130 c, 130 d are open to ambient atmosphere. Located on either edge of wet plate 100 in first and second direction A, B is wet plate wall 117 that has a height X that is greater than or equal to the height Y of channel guides 115. Wet surface 110 may have a layer of wicking material (not shown) for the even distribution of evaporative liquid throughout the surface areas of wet channel 125. As an alternative, wet surface 110 may be sand-blasted or chemically etched to provide a textured surface for the even distribution of liquid. Located substantially midway along the width of each channel guide 115 is notch 135. Notches 135 are axially aligned parallel to longitudinal axis 20.

Also shown in FIG. 3 expanded from core 15 is dry plate 200, which includes an air flow section 202 and an integral refrigerant cooling section 600. Dry plate 200 has substantially the same overall length and width dimensions of wet plate 100. Dry plate 200 has dry side 205 and wet side 210. Projecting from dry side 205 of dry plate 200 are a plurality of substantially parallel heat transfer fins 215 that run the length of dry plate 200 parallel to longitudinal axis 20. In reference to FIGS. 5A-SC, for optimal heat transfer, fins 215 may have variable cross sectional profiles such as cross-fins 215 a shown in FIG. 5A or step-fins 215 b shown in FIG. 5B. Fins 215 c may also be of varying heights as shown in FIG. 5C. Fins 215 cooperate with dry side 205 to define a series of dry channels 225.

Dry channels 225 have air inlet end 230 for accepting air flow along the longitudinal axis 20, from the second direction B to first direction A. On the opposing end is air outlet end 235. Positioned in series along dry channel 225 are ports 242 for the separation and diversion of an air stream to wet side 210. The open area of ports 242 may increase along dry channel 225 toward first direction A in the direction of air flow. The optimal ratio for the area of the largest port opening compared to the area of the smallest port opening is in the range of 1.125 to 2.000 for uniform distribution of air distribution to each wet channel.

Located on both outboard edges of dry plate 200 in the third direction C and fourth direction D are refrigerant cooling sections 600. Refrigerant cooling section 600 is integrally formed with and is a continuous seamless part of dry plate 200. In reference to FIG. 3 and FIG. 5A-C refrigerant cooling section 600 includes a plurality of passageways 610 that are substantially parallel to longitudinal axis 20 and run the length of dry plate 200. Passageways 610 include passageway inlets 612 and passageway outlets 614 for refrigerant flow into and out of refrigerant cooling section 600. Each passageway has a hydraulic diameter in the range of 0.3 to 0.7 mm. Refrigerant cooling section 600 has a substantially planar top surface 620 that is sufficient spaced from dry channel bottom 230 and coplanar with or above fin tips 217. Refrigerant cooling section 600 also has a bottom surface 630 that is substantially co-planer with wet side 210 of dry plate 200.

Referring to FIG. 3, located on wet side 210 of dry plate 200 is distribution conduit 420, which is also integrally formed with dry plate 200. The cross sectional profile of distribution conduit 420 is the same as that of the cross section profile of notch 135 on wet plate 100. Once dry plate 200 is engaged onto wet plate 100, the exterior edge of distribution conduit 420 engages and locks into notch 135 of wet plate 100 for increased structural integrity. Distribution conduit 420 is positioned between the space defined between wet plate 100 and dry plate 200 once the plates are assembled. Shown in FIG. 6, distribution conduit 420 have a series of conduit openings 430 having varying diameter from smaller to larger in the direction of flow. The increasing diameter assists in the proportional distribution of evaporative liquid flow from the distribution conduit 420 to wet channels 125. The optimal ratio for the area of the largest conduit opening 430 a compared to the area of the smallest conduit opening 430 b is in the range of 1.125 to 2.000 for uniform distribution of evaporative liquid to each wet channel.

In reference to FIG. 4, wet plate 100 and dry plate 200 are alternatively positioned and assembled into a stack to form evaporative refrigerant cooler 90. Wet side 210 of dry plate 200 cooperates with wet channels 125 of wet plate 100 to define a plurality of substantially parallel wet air flow conduits 140 extending parallel with latitudinal axis 25. Dry channels 225 cooperate with dry surface 105 of wet plate 100 to form a plurality of substantially parallel dry air flow conduits 240 extending parallel to the longitudinal axis 20. The optimal hydraulic diameter of wet air flow conduit 140 is in the range of 2.0 to 7.5 mm and the optimal hydraulic diameter of dry air flow conduit 240 is in the range of 2.0-5.0 mm for optimal evaporative cooling.

Referring to FIG. 2, in hydraulic communication with passageway inlet 612 of refrigerant cooling section 600 is refrigerant inlet header 310. In hydraulic communication with passageway outlets 614 is outlet header 320 for the collection of cooled refrigerant.

Referring to FIG. 4 once more, a low humidity ambient air stream 500 is induced into dry air flow conduits 240 toward first direction A. As air stream 500 travels along dry air flow conduits 240, ports 242 divert a selected portion of air stream 500 to wet air flow conduits 140. As air stream 500 enters wet air flow conduits 140, air stream 500 is divided into third direction C and fourth direction D. Air stream 500 travels down wet air flow conduits toward wet air outlet 145.

As redistributed air stream 500 flows through wet air flow conduit 140, the relatively low humidity air causes the evaporative liquid to change from a liquid state to a gaseous state. As the physical state of the liquid changes into a gaseous state, the temperatures of wet plate 100, dry plate 200, and air stream 500 are reduced due to the heat absorption by the evaporating liquid.

Some thermal energy from hot refrigerant flowing through refrigerant cooling section 600 is conducted through the body of dry plate 200 and rejected to the dry air flow in dry air conduit 240 with the assistance of fins 215. The bulk of thermal energy from refrigerant cooling section 600 is rejected by forced convection to the cooler wet air stream 500 as it flows over the bottom surface 630 of the refrigerant cooling section 600 through the wet conduits 140.

As the air stream 500 flows down dry air flow channel 240 toward first direction A, the air stream 500 becomes progressively cooler resulting in a temperature gradient where the temperature of the evaporative cooler is lower in the first direction A as compared to the second direction B. As the diverted air stream 500 moves from the latitudinal axis 25 toward wet air outlet 145, the temperature of the evaporative cooler 10 becomes progressively cooler toward the outboard ends. Outlet ends 235 may be blocked to divert all of air stream 500 to wet air flow conduits 140 for maximum cooling of refrigerant as shown in FIG. 2. As an alternative, shown in FIG. 7, outlet ends 235 may be partially unobstructed, whereby conditioned air stream 500 exiting air outlet ends 235 may be used as product air for other purposes such as cooling a room.

In reference to FIG. 4, shown is refrigerant flow in passageways 610 of both outboard refrigerant cooling sections 600 toward first direction A resulting in a co-current flow relative to the flow direction of air stream 500. As an alternative, refrigerant flow in passageways 610 may be toward the second direction B resulting in a counter-current flow relative to the flow direction of air stream 500, which is optimal for heat transfer from the refrigerant. As another alternative, refrigerant flow in one refrigerant cooling section 600 may be in the first direction A, and the refrigerant flow in the other refrigerant cooling section 600 may be in the second direction B resulting in a combination co-current and counter-current flow.

The outboard location of refrigerant cooling section 600 provides sufficient surface area for heat to be released to the exposed end surface 615 by radiation and natural convection to the surrounding environment. Concurrently heat is conducted through dry plate 200 from second and third directions C, D toward longitudinal axis, during which time a portion of heat is released to the cooler air stream 500 in dry air flow conduits 240 with the assistance of fins 215. As air flow 500 flows through wet flow conduit 140, it removes heat by forced convection from the wet side 210 of dry plate 200 and bottom surface 630 of refrigerant cooler 600.

An advantage of the refrigerant cooling section being located outboard of the evaporative refrigerant cooler is that it allows heat to be removed by a combination radiation, conduction, and convection.

Another advantage of the evaporative refrigerant cooler is that the refrigerant cooling section is formed integrally with dry plate 200; whereby, there is no resistance of heat flow from the refrigerant cooling section through the dry plate to the fins for dissipation to air stream in dry flow conduits 240.

Still another advantage of the evaporative refrigerant cooler is that the refrigerant cooling section is formed of a material that is heat conductive and able to withstand the pressure requirements of hot refrigerants.

Yet another advantage of the evaporative refrigerant cooler is that wet plate 100 and dry plate 200 may be formed of a heat conductive material such as copper, aluminum, or brass that allows the plates to be extruded, assembled, and brazed with known methods in the art.

Still yet another advantage of the evaporative refrigerant cooler is that the unit is scalable to be fitted on a roof top or within a motor vehicle, depending on cooling needs.

Another advantage is that the evaporative refrigerant cooler can cool the refrigerant and condition air for another purpose.

While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow. 

1. An evaporative heat exchanger for cooling a refrigerant, comprising: a dry plate having an air flow section and an integral refrigerant cooling section, wherein said airflow section includes a dry side defining a plurality of dry channels in a first direction for air flow and a wet side opposite said dry side, and a series of ports distributed along said dry channel; a wet plate having a wet surface adjacent to and cooperates with said wet side of dry plate to define a plurality of wet channels in a second direction for air flow, wherein each said wet channel is adapted to contain an evaporative liquid and communicates with said dry channel through said ports; and means to distribute said evaporative liquid onto said wet channels; wherein said refrigerant cooling section includes refrigerant passageways, and is disposed outboard of said air flow section and adjacent to an open end section of each said wet channel; whereby air introduced into said dry channels flows through said ports and through said wet channels evaporating said evaporative liquid to enhance cooling of said dry plate and said end section of said wet channels to thereby enhance cooling of said refrigerant cooling section.
 2. An evaporative heat exchanger for cooling a refrigerant of claim 1, further comprising an inlet refrigerant header in hydraulic communication with openings of said refrigerant passageways and an outlet refrigerant header in hydraulic communication with opposing openings of said refrigerant passageways.
 3. An evaporative heat exchanger for cooling a refrigerant of claim 1, wherein said refrigerant passageways have a hydraulic diameter in the range of 0.3 to 0.7 mm.
 4. An evaporative heat exchanger for cooling a refrigerant of claim 1, wherein said dry plates and said wet plates comprises copper, aluminum, or brass.
 5. An evaporative heat exchanger for cooling a refrigerant of claim 1, wherein said dry plates and said wet plates are brazed together.
 6. An evaporative heat exchanger for cooling a refrigerant of claim 4, wherein ratio for the area of the largest port opening compared to the area of the smallest port opening is in the range of 1.125 to 2.000.
 7. An evaporative heat exchanger for cooling a refrigerant of claim 1, wherein said dry plate comprises an integrated evaporative liquid distribution conduit.
 8. An evaporative heat exchanger for cooling a refrigerant of claim 7, wherein said dry plate comprises extruded copper, aluminum, or brass.
 9. An evaporative heat exchanger for cooling a refrigerant of claim 1, wherein said wet surface of wet plate comprises a texture for the wicking of said evaporative fluid.
 10. A plate for an evaporative heat exchange for cooling a refrigerant, comprising: a heat conductive plate having a dry side including an air flow section having a plurality of fins; and a refrigerant cooling section outboard and integral with said air flow section, wherein said refrigerant cooling section includes a plurality of passageways for refrigerant flow.
 11. A plate for an evaporative heat exchanger of claim 10, further comprising a wet side opposing said dry side; wherein said fins are substantially parallel and cooperation with said dry side to form a plurality of substantially parallel dry channels for air flow; and where in said dry channels include a series of ports in hydraulic communication with said wet side.
 12. A plate for an evaporative heat exchanger of claim 11, comprises a first port upstream of air flow and a last port downstream of air flow, wherein said first port has a smaller open area than said last port.
 13. A plate for an evaporative heat exchanger of claim 12, wherein the ratio of said last port open area to said first port open area is in the range of 1.125:1 to 2.0:1.0.
 14. A plate for an evaporative heat exchanger of claim 10, wherein said passageways for refrigerant flow have a hydraulic diameter in the range of 0.3 to 0.7 mm.
 15. A plate for an evaporative heat exchanger of claim 10, further comprising an evaporative liquid distribution conduit.
 16. A plate for an evaporative heat exchanger of claim 15, further comprising copper, aluminum, or brass.
 17. A plate for an evaporative heat exchanger of claim 16, wherein said plate is extruded.
 18. An evaporative heat exchanger for cooling a refrigerant, comprising: a first dry plate having a dry side defining a plurality of dry channels in a first direction and a wet side opposite said dry side, a series of ports distributed along said dry channel, and an refrigerant cooling section comprising refrigerant passageways; a second dry plate having a dry side defining a plurality of dry channels in a first direction and a wet side opposite said dry side, a series of ports distributed along said dry channel, and an refrigerant cooling section comprising refrigerant passageways; and a wet plate having a wet surface adjacent to and cooperates with said wet side of said first dry plate to define a plurality of wet air flow conduits in a second direction adapted to contain an evaporative liquid, each said wet plate further having a dry surface adjacent to and cooperates with said dry side of second dry plate to define a plurality of dry air flow conduits in said first direction, wherein said wet flow conduits communicate with said dry air flow conduits said ports; wherein said refrigerant cooling section is integral with outboard of said dry plate and adjacent to an end section of each said wet channel; thereby providing enhanced heat transfer between refrigerant in said passages and air flow through said wet channel.
 19. An evaporative heat exchanger for cooling a refrigerant of claim 18, where said dry air flow conduit has a hydraulic diameter of 2.0 to 5.0 mm.
 20. An evaporative heat exchanger for cooling a refrigerant of claim 18, where said wet air flow conduit has a hydraulic diameter of 2.0 to 7.5 mm. 